When a surface miner is used as surface mining equipment with a roller-shaped mining member (a frontal mining portion that is attached via a support to a caterpillar) rotatable around its horizontal axis, the mining operation is carried out, in general, according to the so-called cutting operation. According to its basic concept, the mining member of such a device, as is known from, e.g., the patent DE 199 41 801 C2, has a roller width that is greater by a factor of 5 to 8 (as a result of which it can also be defined as a cutting roller as opposed to cutting drill) than that of the cutter loader known from underground mining. The mining member is equipped with bits, and the type of the bits, their number and their arrangement in relation to one another are provided according to the so-called cutting operation. The cutting geometry of each bit is optimized for particular conditions of use. During the separation, each bit creates at the same time a flank for the bit that is displaced in the circumference and follows it in time. The separated material is delivered in the area of the mining member through the screw turns from the outside to the inside to the middle of the turn and subsequently transferred to a removing conveyor. When developing a raw material deposit with a surface miner, the mineral raw materials are mined in blocks. The volume of such a block being mined consists of the mining surface of the mining member, which surface is rectangular in the direction of mining, multiplied by the length of mining. The mining technology for such a device is known from the technical article “Konstruktive und verfahrenstechnische Voraussetzungen und Erfahrungen bei der Eutwicklung eines Surface Miners für den Einsatz in russischen Tagebauen” [Design and technological requirements and experience with the development of a surface miner for use in surface mining in Russia] published in the journal Braunkohle, Surface Mining, Vol. 49 (1997), No. 2, pp. 123 to 128. This includes mining only so many blocks next to one another such that the width of the deposit is reached. The subjacent layer is then mined in turn in blocks located next to each other. The mining member cuts itself free with one or more sides from the rock being mined (formation) during the mining operation with a continuously operating surface miner. This free-cutting is associated with a considerably higher energy consumption and wear and calls for special equipment for the mining member with tools in the edge area compared with the rest of the larger middle area. The technical effort needed for the free-cutting of the mining member at its outer edges increases with increasing hardness of the deposit of mineral raw materials. The separated material is partially thrown out on the side by the edge bits at the outer sides of the mining member in the prior-art mining devices. As a result, accumulations are formed over the entire length of the block being mined. These lead to a reduction in the mining output and require the use of an additional clearing technique. To reduce the accumulations, the surface miner is not operated wit the full roller width on the side of the surface already mined off. As a result, additional losses of output must be accepted. Other drawbacks of such a roller-shaped mining member equipped with round-shaft bits are that high energy losses and intense wear occur on the bits due to the sliding contact of the bits in the case of abrasive earth materials. The specific energy consumption also increases enormously if the compressive strength of the deposits of mineral raw materials is higher than 60 MPa and makes the use of surface miners uneconomical. Another drawback is that pulverized rocks generate increased dust emission during the mining operation. Strong tear-out forces, which lead to the formation of large chunks, are generated on the bits in case of the overshot mining method. This is a considerable obstacle for the entire mechanical mining operation and may lead to a reduction of output, or an additional intermediate breaker becomes necessary.
Disk bits have a rolling contact with the earth material to be mined and subject as a result to a substantially reduced wear compared with the conventional round-shaft bits. The basis for the successful use of the disk bits is the lower tensile strength of the soil compared with the compressive strength, the ratio of the compressive strength to the tensile strength of the soil equaling σc/σt≈10. Due to the use of disk bits, the use of the mining technique can be extended to mineral raw material deposits with a compressive strength of up to 140 MPa. To guarantee the separation in an optimal manner, the rolling disk bits for a surface miner are designed as mini-disk bits and are arranged on the turns of opposite pitch with the driving wedge flanks toward the edges of the tool. As a result, the side forces acting on the tools during the mining operation are eliminated on the two halves of the roller. The conditions of destruction are characterized by substantially higher mining resistances in the edge area because the mining member must cut itself loose at these locations.
Cutter loaders are successfully used in underground mining for mining hard coal, salt and soft ores. The roller-shaped basic body of the cutter loader is equipped with round-shaft or flat bits, which are arranged helically in one or more turns. However, roller-type cutter loaders equipped with disk bits have been known as well. Thus, a cutter loader, over the entire basic body width of which screw turns are arranged and are equipped with disk bits, is known from the article “Walzenschrämlader mit glatten Disken zur Kohlengewinnung” [Roller type cutter loader with smooth disks for mining coal] by Klich A. and Krauze A., published in the journal Bergbau, Vol. 40 (1989), No. 2, pp. 51 to 55. The wedge rings on the disk bits are directed in parallel to the vector of the cutting velocity. Conventional or round-shaft bits with a cutting line distance corresponding to 0.4 to 0.8 times the path distance of the disk bits and with reversed pitch angle are fastened in the edge area, so that the free-cutting of the cutter loader is also guaranteed. The entire cutter loader is fastened to a lifting arm. The disk bits are arranged on the screw turns after the free cut to the half-blocked cut. The separation with a disk type cutter loader follows due to the formation of flanks parallel to the path at right angles to the rock surface, and the specified amount of path is separated or split off in the form of large chips or strips. The path distances of 50 mm to 80 mm are characteristic of earth materials such as coal or salt (compressive strength up to 20-30 MPa). The separation of the specific amount of path follows after a roll-over (primary roll-over). The separated material is loaded on the conveyor through the screw turns. The practical embodiment of this known state of the art is shown in the two drawings on page 53 of the above-mentioned article. The disk bits are fastened with their bit holders on the rotating basic body of the cutter loader of a mining machine. The direction in which the disk bits are mounted and the direction of the screw turns on the body of rotation agree. The number of screw turns depends on the mining output and the characteristics of the earth materials. Radial bits are arranged on the circumference of this cutting disk such that their tips point alternatingly to the outside and toward the cutting roller. As a result, penetration in the rock in place is achieved, and flanks are formed for the disk bits of the wall area. The density of the conventional radial bits in a cutting line is at least twice that of the disk bits. To ensure better ejection of the separated material onto the conveyor, additional loading wedges are provided. The standard width of the cutting roller is in the range of 0.63 m to 1.0 m. During the mining operation, the disk bits thus separate the material in the so-called wall area in the direction of feed, and the parting planes between the wall and the bottom or the roof of the longwall is cut by the lateral closing rings (cutting disks) with the conventional bits. An exact longwall edge is necessary for the normal functioning of the removal and the integrated conveyor. Such disk type cutter loaders are well suited for hard coal with hard inclusions and shelves, because the separation operation follows predominantly by overcoming the tensile strength, and the dust emission is substantially reduced due to the material being in the form of large pieces, and the wear on the bit is substantially reduced as well. Due to its narrow design and because the separated material is conveyed on one side only, as well as due to the arrangement of the disk bits after the free cut (as a consequence of which the bit density is relatively high and there are strong pressing forces), these cutter loaders are not suitable for economical use during the mining of hard and thin layers with surface miners because of the insufficient mining output. The formation of exact longwall edges requires a high bit density on the lateral closing ring. In addition, the use of two types of bits with closing rings is technologically and economically unfavorable.
Furthermore, the concept of a disk roller for the continuous surface miner, which disk roller is arranged in front of the conventional cutting roller equipped with round-shaft bits, is known from the technical article “Einsatzmöglichkeiten des Surface Miners und erste Erfahrungen auβerhalb der Kohle” [Possible applications of the surface miner and preliminary experience outside coal mining], published in the journal Braunkohle, Surface Mining, Vol. 49 (1997), No. 2, pp. 137 to 149 (see FIG. 10). The so-called disk surface miner is the combination of the offset disk row (disk roller) as a main mining unit with a pick-up cutting roller equipped with round-shaft bits. The separated material is sent by this pick-up cutting roller through a chute to a removing conveyor belt in the known manner. The disk bits (also called disks in the source) have a diameter of 430 mm and are arranged on the disk roller in a disk row at a path distance of about 200 mm as well as offset in relation to one another in the direction of mining. All disk bits are continuously in contact with the front being mined during the mining operation and roll at right angles to the surface of the rock. The weight of the surface miner is transmitted uniformly to all disk bits and it thus forms the pressing force. A crushing zone, in which a quasi hydrostatic pressure prevails, is formed under the disk bits. This compressive strain leads to the tensile and shear load on the material under and to the side of the track of the disks. Radial (stress relief) cracks and lateral cracks are formed in the rock formation. These cracks make possible the breaking out of the material to the free surface. Removal that is appropriate for the mining height, precrushing and clearing of the wall surface is accomplished by the pick-up cutting roller. Consequently, two mining members, which are integrated in one machine frame, are necessary for the mining operation. The disk roller has no drive of its own. Considerable pressing forces must be generated to guarantee the separation with the disk bits. It is assumed that the pressing force is generated by the weight of the carrier device and the rolling force by the chassis. The drawbacks of a surface miner based on this concept is that due to the frontal contact of all disk bits with the rock surface with a track distance of 200 mm and rolling over only once, practically no artificial flank can be formed, because a great arc length can be expected in case of a disk diameter of 350-430 mm, which requires an enormously high pressing force for sufficient penetration. Furthermore, the use of two mining members leads to a widening of the distance between the caterpillars and consequently to unfavorable conditions for manoeuvering at the end of the face.